1. Field of the Invention
The present invention relates to a substrate processing apparatus, and in particular to a substrate processing apparatus having a plurality of pusher pins that lift up and lower a substrate.
2. Description of the Related Art
As shown in FIG. 5, there is known a substrate processing apparatus 52 that has a processing chamber (not shown) in which a wafer W as a substrate is housed and the wafer W is subjected to predetermined processing, a stage 50 that is disposed inside the processing chamber and on which the wafer W is mounted, and a plurality of pusher pins 51 that can be made to project out from the stage 50. The pusher pins 51 are rod-like members penetrating through the stage 50 and disposed on an arm 53 disposed below the stage 50. The arm 53 is moved upward and downward by a motor 54. Thus, the pusher pins 51 are also moved upward and downward (see, for example, Japanese Laid-Open Patent Publication (Kokai) No. 2002-134489).
As methods of disposing the pusher pins 51 on the arm 53, there are known a method in which the pusher pins 51 are fixed to the arm 53 (hereinafter referred to merely as the “fixing method”), and a method in which the pusher pins 51 are supported by the arm 53 without being fixed to the arm 53 (hereinafter referred to merely as the “supporting method”). In the fixing method, the upward/downward movement of the pusher pins 51 is restricted by the arm 53. In the supporting method, the upward movement of the pusher pins 51 is restricted by the arm 53, but the downward movement of the pusher pins 51 is not restricted by the arm 53, and the pusher pins 51 move down under their own weight or the like.
In recent years, there may be a case where a pressure difference is produced in the processing chamber. Specifically, there may be a case where the pressure above the stage 50 is higher than the pressure below the stage 50. In this case, to prevent gas above the stage 50 from leaking to below the stage 50 via the pin through holes 55 of the stage 50 to eliminate the pressure difference, the pin through holes 55 have to be sealed. In general, to seal each pin through hole 55, an O-ring is disposed in a part of the pusher pin 51 which is housed in the pin through hole 55, and hence the O-ring is interposed between a side face of the pin through hole 55 and a side face of the pusher pin 51.
However, when the stage 50 has a heater incorporated therein, and the heater heats the wafer W, the above-mentioned gap may be narrowed due to a difference in the amount of thermal expansion between the stage 50 and the arm 53, causing the O-ring to be excessively compressed. Once the O-ring has been excessively compressed, it cannot restore, and as a result, cannot seal the pin through hole 55.
In recent years, a method in which a pin through hole is sealed without providing an O-ring in the above-mentioned gap has thus been studied. Specifically, as shown in FIG. 6, a flange 60a is formed part way along a pusher pin 60 in a manner extending vertically to the direction in which the pusher pin 60 moves upward and downward, and on the other hand, a stage is provided with a seal surface 61 parallel to the flange 60a, and an O-ring 62 is disposed on the seal surface 61.
In this method, when the pusher pin 60 has moved down, the flange 60a comes into abutment with the O-ring 62 and compresses the O-ring 62. Therefore, a gap between the flange 60a and the seal surface 61 is sealed, and as a result, a pin through hole 63 is sealed.
However, in the method of FIG. 6, when the pusher pin 60 is fixed to an arm 64, the O-ring 62 may be excessively compressed or not be compressed due to a difference in the amount of thermal expansion between the pusher pin 60 and the stage in the vertical direction as viewed in the drawing, and hence the pin through hole 63 may not be properly sealed.
Moreover, when the pusher pin 60 is supported by the arm 64 without being fixed to the arm 64, the downward movement of the pusher pin 60 is not restricted by the arm 64, and hence, when the pusher pin 60 comes into abutment with the side face of the pin through hole 63, the pusher pin 60 does not move down. Also, the failure of the pusher pin 60 to move down cannot be detected. If the pusher pin 60 does not move down, the O-ring 62 is not compressed, and hence the pin through hole 63 cannot be properly sealed.